1. Field of the Invention
The present invention relates to a laminate type band pass filter to be used for a microwave band and a diplexer using the same.
2. Description of the Related Art
Structures using via holes as inductor conductors of a resonator have been proposed for filters including a resonator formed by laying a plurality of dielectric layers one on the other have been proposed.
More specifically, Patent Document 1 (Japanese Patent No. 3,127,792) proposes an LC filter including a plurality of dielectric layers that are laid one on the other, a plurality of inductors formed by means of via holes running through the plurality of dielectric layers in the layering direction and a plurality of capacitors, each being formed between capacitor electrodes formed among the plurality of dielectric layers, the inductors being arranged in a direction orthogonal relative to the main surfaces of the capacitor electrodes, the plurality of inductors and the plurality of capacitors being respectively connected in parallel, a plurality of LC resonators being formed by the plurality of inductors and the plurality of capacitors, the plurality of inductors of the plurality of LC resonators being electromagnetically coupled.
Patent Document 2 (Jpn. Pat. Appln. Laid-Open Publication No. 2003-124769) proposes a laminate type LC filter including an input terminal, an output terminal, at least two LC resonators electrically connected to the input terminal and the output terminal, an input side LC trap circuit electrically connected to between the input terminal and the LC resonators and an output side LC trap circuit electrically connected to between the output terminal and the LC resonators, part of the inductor forming the LC resonator electrically connected to the input terminal being commonly used as part of the inductor forming the input side LC trap circuit, part of the inductor forming the LC resonator electrically connected to the output terminal being commonly used as part of the inductor forming the output side LC trap circuit. The Patent Document 2 discloses that the inductors of the LC resonators and the LC trap circuits are formed by means of via holes running through a plurality of dielectric layers in the layering direction.
FIG. 1 of the accompanying drawings is an equivalent electric circuit diagram of a laminate type LC filter 100 disclosed in the Patent Document 2, and FIG. 2 is an exploded schematic perspective view of the laminate type LC filter that is illustrated in FIG. 1.
Referring to FIG. 2, the laminate type LC filter 100 includes an insulator sheet 103 having a coupling capacitor 110 arranged on the surface thereof, an insulator sheet 104 having resonator capacitors 111 and 112 arranged on the surface thereof, insulator sheets 106, 107 respectively having LC trap capacitor conductors 113, 114, 115 and 116 arranged on the surfaces thereof, insulator sheets 105 and 108 respectively having inductor via holes 117b, 118b, 117e and 118e and insulator sheets 102, 109 respectively having grounding conductors 119 and 120 on the surfaces thereof.
Inductor via holes 117a through 117e and inductor via holes 118a through 118e that operate as resonator coil conductors are successively connected to each other in the layering direction of the insulator sheets 102 through 109 to form resonator inductors L101 and L102 substantially having an effective length of λ/4. The axial direction of the resonator inductors L101 and L102 are perpendicular to the surfaces of the insulator sheets 102 through 109.
On the insulator sheet 104, the drawn out part 111a of the resonator capacitor conductor 111 is exposed to the left side and connected to the input terminal while the drawn out part 112a of the resonator capacitor conductor 112 is exposed to the right side and connected to the output terminal.
Referring to FIG. 2, the resonator inductor L101 and the resonator capacitor C101 form a parallel resonance circuit and hence an LC resonator Q101. Similarly, the resonator inductor L102 and the resonator capacitor C102 form a parallel resolution circuit and hence an LC resonator Q102. The LC resonators Q101 and Q102 are electrically connected to each other by way of a coupling capacitor C103 to form a two-step band pass filter. The part L101a of the resonator inductor L101 and the LC trap capacitor C104 form an input side LC trap circuit T101. Similarly, the part 102a of the resonator inductor L102 and the LC trap capacitor C105 form an output side LC trap circuit T102.